A recent wind power generator has a creeping discharge element on its windmill blade to increase a rotational force (lift) of the blade. The creeping discharge element is driven by power supply circuits including a switching circuit for converting a DC voltage into an AC voltage by a switching operation, a resonant reactor, and a high-voltage transformer for AC voltage boosting. The power supply circuit uses a resonance, which is generated by the resonant reactor and a capacitive component of the creeping discharge element, to apply a high-frequency high-voltage to the creeping discharge element, thus generating a streamer. This gives the lift to the blade.
The wind power generator is installed outdoors, so its installation environment greatly influences on the electrical performance of the creeping discharge element exposed on the blade. For example, the capacitive component of the creeping discharge element greatly varies according not only to the installation environment but also to a growth state of the streamer during the discharge.
The creeping discharge element is a discharge load having high nonlinearity, and its performance change causes the circuit for driving the creeping discharge element overloaded to generate heat. Insufficient cooling of the generated heat may lead to, for example, the overcurrent in the power supply circuit or a breakage of the creeping discharge element caused by overheating.
Thus, a conventional power supply circuit limits power, which is determined by voltage and current, and restricts a resonant period within a predetermined range.
The creeping discharge element of the wind power generator, which is installed outdoors, may get wet due to rainfall, at startup time or during the discharge, to increase its load capacitance. This leads to the resonant period out of the predetermined range to overload the circuit. Such environmental conditions should be considered.
A considerable measure detects an environmental state of the creeping discharge element with a rainfall detector and controls the circuit so as to stop a power supply to the creeping discharge element when detecting rainfall. This, however, increases a cost for additional installation of a device such as the rainfall detector.